The present invention relates to a method for forming a cast-in-place support column below the surface of the ground. In particular, it relates to a method for forming cast-in-place concrete piles by driving into the ground a driving foot coupled to a hollow driving mandrel to form the bore hole with the mandrel having radial apertures in the lower section and introducing concrete under pressure into the hollow portion of the mandrel so that the some of the concrete is conveyed through the apertures into the area (i.e., annulus) between the surfaces of bore hole and the mandrel to prevent the ground from collapsing around the mandrel.
Foundation piles, or support columns, are typically utilized in supporting structures such as bridges, piers, and buildings. Support columns or piles are preferably formed of concrete and utilize a minimum of steel reinforcing members. A bore is formed in the ground of the desired depth, and concrete fill material is then introduced into the bore thus formed and allowed to cure or harden.
A number of prior art methods and apparatus have been proposed for forming a cast-in-place support column. A method is disclosed in U.S. Pat. No. 3,638,433 to Sherard. Sherard discloses forcing a mandrel with a drive foot into the soil to form a space with a cross section greater than the mandrel in the wake of the drive foot and filling this space with concrete supplied at the ground surface with the concrete flowing downwardly along the mandrel behind the drive foot. In some cases the mandrel is detachable from the drive foot and removed prior to the concrete hardening. In other cases the mandrel is left as a part of the structure.
U.S. Pat. No. 3,851,484 to Steding discloses a hopper for containing the concrete. The mandrel is driven through an aperture in the bottom of the hopper with the concrete flowing through the space between the mandrel and the aperture walls. Steding shows a mandrel in FIG. 2 which is hollow and has a plurality of radial apertures 52. These radial apertures extend along the entire length of the mandrel and are designed to permit the flow of concrete in the space between the mandrel and the surface of the bore hole and into the hollow interior of the mandrel. Concrete is basically supplied by gravity from a hopper on the surface to the outside of the mandrel and in the case of a hollow mandrel to the interior of the mandrel through radial apertures.
U. S. Pat. No. 4,018,056 to Poma discloses a pile driving apparatus with a mandrel that is driven through a discharge opening of a fill hopper. Concrete flows through this opening and into the pile-forming hole as it is being formed. The mandrel has apertures so that concrete can flow into the interior of the mandrel.
U.S. Pat. No. 3,851,485 to Steding discloses a hollow mandrel with radial apertures in FIG. 29. It too is designed for the concrete to be supplied by gravity into the space between the mandrel and the surface of the bore hole with the interior of the mandrel being filled with concrete through the radial apertures.
U.S. Pat. No. 4,152,089 to Stannard discloses the method for introducing liquified fill material into the mandrel under pressure. The hollow mandrel and driving foot are driven in the normal manner. When the desired depth has been reached, fill material is introduced under pressure to the bottom hollow portion of the mandrel. In this way the pressure from the liquified fill material is used to extract the mandrel from the bore hole and to fill the bore hole with concrete. The partition plate provided in the bottom portion of the mandrel has an aperture connected to a conduit for the fill material passing through the partition plate.
U.S. Pat. No. 3,925,998 to Le Corgne discloses using a hollow mandrel with radial apertures which is driven through a hopper box. The fill material flows along the outside of the mandrel into the bore hole and enters the inside of the mandrel through the radial apertures.
One of the problems encountered in driving piles is the constriction of the pile near the bottom as it is being driven. As the driving foot is driven into the ground, forces emanating from the foot cause the ground directly beneath the foot to rotate out from under the foot and to continue to rotate until they act inwardly on the pile hole surface some distance above the location of the foot. When concrete is gravity fed into the area between the mandrel and the surface of the pile hole, the concrete has a tendency to prevent this from occurring. The extent to which it prevents this from occurring is dependent upon the head pressure of the concrete and the forces emanating from the foot. Unfortunately, in many cases the head pressure of the concrete is not sufficient to prevent the constriction of the pile. Constriction is likely to be greater in some of types of soil than others. It becomes a particularly acute problem in some types of clay.
Another problem encountered with a pile where the concrete is gravity fed along the outside of the pile is that a large amount of concrete can be wasted when driving through porous material such as sand. Gravity filling of concrete must occur through the entire driving operation in order to ensure that an adequate amount of concrete is contained in the bottom of the pile. Thus, in driving through a section of porous sand the concrete must continue to be poured into the hole, and it will spread out through the sand formation and not increase the strength of the pile.
The object of the present invention is to develop a method for formation of cast-in-place columns so that the constriction of the pile is minimized. Another object of the invention is the development of a method of preventing the loss of a large amount of concrete while driving a pile through porous structure such as land fill or cavernous limestone.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed desciption, taken in conjunction with accompanying drawings illustrating the preferred embodiments of the invention.